An optical pickup device is routinely used for writing information signals on an optical recording medium, such as an optical disc, and for reading out the information signals recorded on this recording medium. This type of the optical pickup device includes a main body unit, provided with a light source, such as a semiconductor laser, and with a light receiving element, such as a photodiode, an objective lens, on which falls a light beam radiated from the light source, and a driving mechanism for deflecting this objective lens in a preset direction, which will be explained subsequently.
This objective lens driving mechanism supports an objective lens, adapted for converging the light beam, radiated from a light source, along a direction of the optical axis of the objective lens, that is in the focusing direction, and along a direction perpendicular to the optical axis, that is in the tracking direction, while causing the objective lens to be deflected by an electromagnetic actuator in the focusing and tracking directions. The objective lens driving mechanism causes movement of this objective lens to be moved along the direction of the optical axis of the objective lens and along the direction perpendicular to the optical axis to cause a light spot formed by this objective lens on a signal recording surface of the optical recording medium to follow a recording track on the signal recording surface of the optical recording medium. That is, the objective lens driving mechanism causes the objective lens to be moved along the direction of the optical axis of the objective lens, that is in the focusing direction, to execute focusing control of converging the light beam radiated from the light source on the signal recording surface. The objective lens driving mechanism also causes the objective lens to be moved in the focusing direction along the optical axis of the objective lens, and in the tracking direction, that is in a direction perpendicular to the tangential line of the recording track, to cause a light converging point of the light beam radiated from the light source to follow the recording track, by way of performing tracking adjustment.
The objective lens driving mechanism includes a stationary unit, mounted on the main body unit, a lens bobbin, carrying the objective lens, and a supporting member interconnecting the stationary unit and the lens bobbin. The supporting unit is made up by four flexible fine linear members and supports the lens bobbin for movement along the direction parallel to the optical axis and along the direction perpendicular to the optical axis with respect to the stationary unit. That is, each of the linear members making up the supporting unit has its one end mounted on the stationary unit, while having its other end mounted on the lens bobbin.
The stationary unit is provided with a magnetic circuit unit comprised of a magnet and a yoke. On the lens bobbin are mounted a driving coil for focusing and another driving coil for tracking, both mounted in a magnetic field generated by a magnet constituting the magnetic circuit unit. In this objective lens driving mechanism, when the current is supplied to the driving coil for focusing, the driving coil for focusing is moved, along with the lens bobbin, along the direction of the optical axis of the objective lens, together with the lens bobbin, under the interaction with the magnetic field generated by the magnetic circuit unit. When the current is supplied to the driving coil for tracking, the driving coil for tracking is moved, along with the lens bobbin, in the direction perpendicular to the optical axis of the objective lens, along with the lens bobbin, under the interaction with the magnetic field generated by the magnetic circuit unit. By this interaction between the respective driving coils and the magnetic circuit unit, focusing control and tracking control are executed so that the light spot of the light beam radiated from the light source and converged on the signal recording surface by the objective lens will follow up with vertical movement of the signal recording surface and with the recording track.
In this objective lens driving mechanism, current supply to the respective driving coils is via the respective linear members forming the supporting unit. Consequently, these linear members are desirably formed of a material which is low in electrical resistance and which does not produce resonance in the frequency range used, for example, such a material as beryllium copper. Meanwhile, these linear members are of a thickness of the order of 80 μm, a width up to 80 to 90 μm and a length of the order of 15 to 20 mm.
In the above-described objective lens driving device, since the four linear members forming the supporting unit are used as feeder lines for the driving coil for focusing and for the driving coil for tracking, and hence need to be electrically independent of and electrically insulated from each other. Therefore, the linear members forming the supporting unit must be formed as respectively separate members.
These linear members were difficult to form to high precision in a manner free from distortion or flexure. These linear members are formed by first punching a plate member, and by providing a unit comprised of plural linear members 101, 101 lying within a frame-shaped frame 102, with the ends of the linear members being secured to the inner side edges of the frame 102, as shown in FIG. 1. The linear members 101, 101 then are severed from the frame 102. However, when severed from the frame 102, the linear members 101 tend to be distorted or flexed.
It may be contemplated to interconnect both ends of the two linear members 101, 101, neighboring to the objective lens driving mechanism, by synthetic resin components 103, 103, by insert molding, as the plural linear members 101, 101 are supported by the frame 102, thereby suppressing torsion or flexure of the linear members 101, 101. In this case, both ends of the two linear members 101, 101 are severed from the frame 102, as both ends of the linear members 101, 101 remain connected to the synthetic resin components 103, 103. The resulting unit is used in this state as the objective lens driving device. If the linear members 101, 101 are connected by the synthetic resin components 103, 103 to the frame as described above, the resulting unit becomes thicker than the liner members per se. The unit carrying the linear members 101, 101 thus connected is locally different in thickness, so that, if a plural number of such units are stacked directly together, the linear members 101, 101 tend to be deformed. For transporting the units, carrying the linear members 101, 101, thus connected, in a state of preventing the linear members 101 from becoming deformed, dedicated packing materials need to be used. If a large number of the units, carrying the linear members 101, 101, are to be packaged and transported, the packages for transport, employing the dedicated packaging materials, are bulky in size, to render it impossible to improve the transport efficiency.
Moreover, beryllium copper, retained to be convenient as a material forming the above-mentioned linear members, is difficult to procure, while being costly.